Competing technology can be divided into two categories. The first category includes conventional toplighting with rectangular roof skylights, clerestories, roof monitors, roof windows, and tubular skylights, the latter known generically as tubular daylighting devices (TDDs). Some problems exhibited by most of these include:
1. Glare potential, from direct beam sunlight entering the space in such a way that people can see this very bright light directly (and indirectly by reflection from surfaces in the room).
2. Solar overheating, resulting from large aperture areas not moderated by heat shading or reflecting surfaces or shades.
3. Wintertime heat loss by conduction, convection, and radiation of room heat upward through the skylight to the outdoors, especially troublesome on cold winter nights.
4. A common need for custom architectural work, to adjust the building design to accommodate the daylighting system without excessive glare or overheating, this adding to the cost and complexity of the installation.
5. Spatially non uniform illumination over the space.
6. Temporally non uniform illumination over the course of the day, as the sun rises, moves through the sky, and sets.
One or Two-Axis Tracking
The second category of potentially competing technology, based on one or two-axis tracking designs, utilizes concentrating solar collectors of the “dish” reflector or Fresnel lens type, coupled with sophisticated optical systems to capture the concentrated solar flux and put it into light pipes for distribution to building spaces. Some of the distribution systems utilize solid or liquid light pipe media, such as fiber optics. Some of the problems exhibited by prior art daylighting systems include:
1. High expense for the design and manufacture of the high-quality optical components, such as primary mirrors, lenses, or special non-imaging concentrators, and relay mirrors and lenses.
2. High expense for the complex mechanisms required to track the sun via the primary mirror in both azimuth and altitude.
3. High expense to design and fabricate the building to accommodate these complex optical systems.
4. Propensity for tracking mechanisms to fail when exposed to the sun and weather.
5. Light losses, both in flux transmitted and color distortions, associated with absorption of light flux as it travels through solid or liquid media.
6. Tracking mechanisms often require high accuracy and must be calibrated to and maintain tight tolerances
The primary problem with TDDs and horizontal rectangular-aperture roof skylights is that as the sun's altitude angle (angular distance above the horizon) decreases, the effective size of the device's entrance aperture decreases as well, so that less flux is captured by the device (while the potential heat loss remains high, especially for large aperture skylights). Furthermore, as the solar altitude decreases, the angle of incidence on the wall of the reflective light tube (or the skylight well or shaft) also increases, thereby increasing both flux absorption per reflection and the number of reflections for a ray of sunlight to propagate down the tube to the space below. The result is a substantial decline in skylight illumination performance with solar altitude angle.
In order to capture enough diffuse sky light flux at low sun angle (mornings and afternoons), both TDD and conventional skylight apertures have to be increased. With these enlargements also come increases in heat flux into and out of the building through the skylight by the mechanisms of radiation, conduction, and convection.
Sidelighting from windows in walls is not included in the above competing options because it is not available for the core spaces of buildings, far removed from an exterior wall, the subject of this application is also intended to provide daylight illumination to areas adjacent to the window when for various reasons the window illumination is inadequate, and because this invention is also intended to provide daylight illumination to both spaces distant from a window wall and windowless building spaces even when they are adjacent to an exterior wall.
The prior art includes conventional rectangular- and round-aperture roof skylights, including those with planar, domed, and pyramidal glazing made of glass or transparent plastic, and tubular daylighting devices of all kinds. Specific patents more closely allied with the current application are listed below.
U.S. Pat. No. 5,493,824 issued to Lee Webster on Feb. 27, 1996 describes a system whereby a glazed aperture faces the sun and is tracked in azimuth. It also contains reflective vanes behind the glazing which redirect incident direct beam sunlight downward into the room below. The vanes also are adjusted to optimize performance as the sun moves up and down relative to the device. The device described includes a housing with an opening for receiving sunlight. The opening is covered with an ultraviolet-deflecting lens and the housing contains reflectors which direct sunlight through a conduit to a diffuser. The housing rests upon and is rotatable with respect to an annular base. A horizontal sensor arrangement controls rotational movement of the housing with respect to the base to maintain optimum horizontal alignment of the reflectors with respect to the sun. A vertical sensor arrangement causes vertical angular movement of the reflectors to maintain optimum vertical alignment of the reflectors with respect to the sun. The light conduit contains an infrared-deflecting lens to filter out infrared radiation. A dead air space placed in the light conduit prevents heat transfer as light is transmitted along the conduit.
U.S. Patent Publication No 2004/0118447 by Muhs is similar to U.S. Pat. No. 6,128,135 issued to Stiles et al. on Oct. 3, 2000 because the principles of operation and much of the optics are quite similar. The difference is that Muhs lacks a tertiary reflector, which in the Kinney case is planar. Instead, the Muhs patent sends the light from the secondary mirror to a flexible fiber optic bundle, an expensive option with potential optical problems. There could also be differences in the shapes of the primary and secondary mirrors between the two patents. The Kinney primary mirror is concave parabolic and the secondary is convex parabolic.
U.S. Patent Publication No. 2004/0050380 by Hiroshi Abe shows an electronic diagram that has reflective vanes which track in azimuth and that the vanes are tilted from the vertical by varying amounts. The purposes of the vanes are different in the two designs. In the Abe patent, these vanes are the primary reflecting means to redirect sunlight downward into the room below. The second two-axis tracking system has no multiple tracking reflecting vanes.
U.S. Pat. No. 6,691,701 issued to Roth on Feb. 17, 2004 is nearly duplicate of the '139 tracking patent, in having a primary mirror with a hole in it, a secondary reflector, and a tracking planar tertiary reflector sending a beam of concentrated sunlight vertically downward into a light pipe.
U.S. Pat. No. 6,557,804 issued to Carroll May 6, 2003 is intended for space propulsion, not for illumination and shares no similarity with the current application, except possibly through the gear and motor rotating mechanism.
U.S. Pat. No. 6,299,317 issued to Gorthala on Oct. 9, 2001 is a clever design involving components that have been known generically for some time, but has limitations mainly due to the large spread of the rays emerging from the secondary concentrator into the optical fiber, meaning that many of the rays from the concentrator will be incident at large angles on the fiber entrance aperture and will undergo many reflections and increased path lengths through the optical fiber, causing substantial losses along the way. Heating of the optical fiber through absorption when the sky is clear and with high concentration ratios is a problem noted by other experimenters attempting to use solid light pipes in similar applications.
U.S. Pat. No. 5,907,648 issued to Miller on May 29, 1999 describes a beam fiber optic spotlight luminaire and U.S. Pat. No. 4,720,170 issued to Learn discloses tracking primary and secondary mirrors, like the Muhs patent, sending concentrated beam sunlight into a fiber optic or other flexible light pipe and suffers from the problems of such mentioned in the description the 2004/0118447 publication. The patent's FIG. 2 offers a methodology for ameliorating the problem by passing the captured concentrated beam sunlight through a column of clean water, thereby stripping off much of the infrared portion of the solar spectrum, as described in McCluney, Ross, “Color-rendering of daylight from water-filled light pipes,” Solar Energy Materials, Vol. 21, 2-3 Dec. 1990, pp. 191-206. FIG. 3 offers a methodology similar to the Stiles patent for directing the concentrated daylighting into a light pipe, but this method requires a flexible light piping system to accommodate declination changes and places the planar reflector in front of the primary mirror. This is an equatorial design requiring seasonal adjustment of the declination but which tracks around an axis through the light pipe on a daily basis. This patent offers the unique characteristic of claiming a military use of solar energy. A means of switching between solar and electric lighting is claimed but insufficiently described.
U.S. Pat. No. 4,429,952 issued to Dominguez is the one known commercially as the “Sol-Luminaire” skylight, a skylight with a tracking planar mirror above it. This is a closed loop design, it obtains feedback from the position of the sun and corrects itself based on this feedback. This method can be fooled by passing clouds.
U.S. Pat. No. 4,389,085 issued to Mori on Jun. 21, 1983 is a daylighting system that was promoted for a while a decade or two ago. It suggests a variety of means for collecting sunlight and distributing it to interior spaces. All are relatively high-tech in nature and generally are expected to be expensive. No control system is claimed. The unconventional Fresnel-lens-like drawings are clever and interesting, but probably more artistic in use than practical.
U.S. Pat. No. 4,246,477 issued to Latter on Jan. 20, 1981 is an equatorial tracking Fresnel lens plus reflectors and piping system with lenses for refocusing the solar beam for long-distance piping and distribution into buildings. The Fresnel lens as shown is too small to deliver useful illumination to all but a tiny area of a building. Scaling it up to large enough size to be useful might be possible, but expensive. The extensive piping system in particular, with associated high-quality optical components, should prove very expensive and economically prohibitive.
U.S. Pat. No. 4,086,485 issued to Kaplow in 1978 suggests the use of an array of apparently small Cassegrain telescopic systems with primary and secondary mirrors, meaning that the whole system requires tracking, apparently for focusing solar radiation onto small photovoltaic sensors for the generation of electricity. No means for illumination distribution are shown in the drawings and the means of tracking is not very clear. This patent has a closed loop system for tracking.